The embodiments described herein relate to an X-ray detector and an X-ray CT (computed tomography) apparatus, and more particularly to an X-ray detector using a semiconductor which directly converts photons of X-rays into electrical signals and an X-ray CT apparatus having such an X-ray detector.
In an X-ray CT apparatus, an X-ray source and an X-ray detector opposite to each other scan a subject to collect projected data, and reconstructs an image on the basis of the projected data. Some X-ray CT apparatuses perform imaging targeted on a specific element by utilizing the difference among elements in the energy-dependence of the X-ray absorption coefficient.
Such an X-ray CT apparatus uses an X-ray detector which counts the photons of X-rays energy by energy. In such an X-ray detector, a semiconductor directly converts photons of X-rays into electrical signals. As the semiconductor, CZT (cadmium zinc telluride) or the like may be used for instance.
In an X-ray detector using such a semiconductor, as the photon count becomes saturated when the flux rate of X-rays becomes high, multiple detecting layers are provided to raise the saturation limit (see U.S. Patent Application No. 2006/0056581 for instance).
Since the saturation limit of photon count is determined by the thickness of each layer in an X-ray detector having multiple semiconductor layers, the manufacture of such X-ray detectors requires sophisticated manufacturing technology and precision manufacturing equipment. For this reason, such X-ray detectors inevitably cost high.
Accordingly, it is desirable to provide an X-ray detector which is adaptable to low to high flux rates with only one layer of semiconductor and an X-ray CT apparatus having such an X-ray detector.